June 6, 2003
Algal Bloom of non-toxic Gyrodinium uncatenum causing deep-brown water color in St. Martin River.

A water sample was collected by the Maryland Department of Natural Resources at the upper St. Martin River continuous monitoring site during routine water quality monitoring on 6/5/2003. The non-toxic dinoflagellate Gyrodinium uncatenum was found blooming at 118,000 cells/ml giving the water a dark chocolate brown appearance. We have a picture of two water samples from the Coastal Bays comparing the water color of the bloom (left) with a sample from a non-bloom location on Turville Creek (right).

Evidence of the bloom and its effects on water quality can be seen with Graph of dissolved oxygen levels at Bishopville Prong between 5/29 and 6/4.the Bishopville Prong Continuous monitoring station data. Dissolved oxygen levels have been swinging between supersaturation near 200% of normal on 6/2/03 through 6/3/03, then declining briefly to 0% on 6/4/03 as the biology of the bloom consumes oxygen to levels unfit for Bay life. The pH levels increase during severe blooms and the data on 6/2/03 and 6/3/03 increase above 8 at the same time chlorophyll levels, an index of the amount of algae in the water rise above 500 ug chlorophyll/L. Values above 100 ug chlorophyll/L are indicative of severe blooms.


Graph of pH levels at Bishopville Prong between 5/29 and 6/4.Graph of Chlorophyll a levels at Bishopville Prong between 5/29 and 6/4.

A photo of 2 water samples from the Coastal Bays. The sample on the left is of the dark-brown algal-bloom waters from XDM4486, the sample on the right is from TUV0016 where there was no bloom.
Comparison of a sample of the dark brown algal-bloom waters from the Upper St. Martin River (Station XDM4486) versus non-bloom water of Turville Creek (Station TUV0016) on June 5, 2003. The concentration in the bloom sample was 118,000 cells/ml of the non-toxic dinoflagellate Gyrodinium uncatenum.